core practice · coding problem
Kth largest element with a heap
Return the k-th largest element of an unsorted array using a heap, without fully sorting.
The mechanism
A heap gives you the min or max in O(1) and re-balances in O(log n). Whenever a problem says "top k", "k-th largest", or "merge k sorted", a heap of size k is usually the answer — far cheaper than sorting everything.
Expected evidence
findKthLargest([3,2,1,5,6,4], 2) -> 5
Try this drill in the practice workspace →
Hints when you need them
- Keep a min-heap of size k; the root is the answer.
- If the heap exceeds k, pop the smallest.
Watch for these mistakes
- Sorting the whole input when a size-k heap suffices
- Inverting heap polarity: top-k smallest wants a size-k max-heap (evict the largest), top-k largest wants a size-k min-heap
- Forgetting most languages give a min-heap by default